(_c_) A sheet of non-cohesive gold, No. 4, is laid on a sheet of tin of the same number, cut into strips and rolled into cylinders, or folded into blocks, always in equal portions; then they will unite to the extent of two leaves. These fillings sometimes become a solid mass about the color of amalgam, and last very well, as the metals have become united by electrolysis. An excess of tin will be marked by lines or pits in the filling, showing where the tin has been disintegrated or dissolved by the chemical action which occurs on the surface exposed to moisture. No doubt, good fillings have been made by the above methods, yet some were granular, gritty, and were easily removed, while others were quite smooth and hard; probably in the first instance the proportion of tin and gold was not proper,--that is, not equal; or it was not well condensed. Tin being the positive element, it is more easily acted on and disintegrated by electrolysis (chemical action of the fluids). When this combination does become hard, it wears longer than tin on an occlusal surface, but we believe that in some cases where it was used the teeth could have been saved just as well with either tin or gold, or by filling part of the cavity with tin and the rest with gold. If tin foil is laid on 22-carat gold and vulcanized, it becomes thoroughly attached and will take a tin polish; the attraction or interchange of atoms takes place to this extent. This combination of tin and gold can be used at the cervical margin, or a cavity can be lined with it, and the remainder filled with cohesive or non-cohesive gold.